Selectively adjustable, lockable hinges are generally well known. In essence, such hinges consist of a pair of hingably interconnected members mutually relatively rotatable about a common pivot. Prior locking devices typically include those having a pawl, which is pivotally connected to one hinge member, and which can be rotationally biased about its pivot by way of a cam acting on a cam follower surface of the pawl thereby rotating the pawl into interferring relation with teeth arranged around an arcuate portion of the other member. As a result the locked hinge is secured in locked relation by a balanced distribution of forces between the pivots of the cam, the locking pawl, and the hinge.
In many applications, including by way of example and without limitation, automobile seat back hinge applications, there is a requirement for the two members of the hinge to be rigidly locked, with a minimum of play. One element of "play" results from clearances that are necessarily a part of any device containing parts adapted for mutually relative movement. "Clearance" is the difference in size between mating parts prior to their assembly. Typically the clearance on cylindrical parts may be expressed as radial clearance or diametrical clearance. Positive clearance implies that the inside dimension of the female part is larger than the corresponding outside dimension of the male part. In typical mechanical applications a running fit requires about 0.001 inches of radial clearance for a one inch diameter shaft. A clearance of 0.003 inches on a one inch shaft is considered to be a loose fit. In typical automotive seat back hinge manufacturing, mass production processing techniques often result in clearances of 0.008 inches.
The amount of clearance typically found in seat back hinges of the type above-described, introduce an element of play called "chuck" into the mechanical system of which the hinge is a part. Note that "chuck" is not the "play" which is introduced through the flexure of any mechanical components. Rather, the term is expressly used and understood in the automobile seat back art to mean the component of play which results from mechanical lost motion due to clearances between interconnected parts, when leverage forces are applied across the hinge.
"Chuck" is a highly undesirable characteristic in automobile seat back hinges, for both safety and aesthetic reasons. In any case, considerable energy has been applied in the past in search of ways to reduce and preferably minimize "chuck".